Symbol’s function definition is void: first

[AnabasisXu]

Error message:

emmet-expr-on-line: Symbol’s function definition is void: first

It points to the following function, but I could not find any way to track the definition of the function first.

(defun emmet-expr-on-line ()
  "Extract a emmet expression and the corresponding bounds
   for the current line."
  (let* ((end (point))
         (start (emmet-find-left-bound))
         (line (buffer-substring-no-properties start end))
         (expr (emmet-regex "\\([ \t]*\\)\\([^\n]+\\)" line 2)))
    (if (first expr)
        (list (first expr) start end))))

Solved:
the problem is caused by the fact that first second third fourth fifth sixth need to be updated to cl-first...cl-sixth